Methods and apparatus for buffering parenteral solutions

ABSTRACT

A system for transferring solutions from a first cartridge into a second cartridge comprises a cartridge holder, a plunger driver, and a cartridge connector. The cartridge connector carries a transfer needle and an exhaust needle. The cartridge holder positions the first cartridge against the cartridge connector so that the transfer needle penetrates the first cartridge septum. The second cartridge is removably inserted into another end of the cartridge connector so that both the transfer needle and the exhaust needle penetrate the second cartridge septum. The plunger driver is disposed to advance a plunger on the first cartridge to transfer solution from the first cartridge into the second cartridge thus displacing solution from the second cartridge through the exhaust needle. The cartridge connector includes a sealed interior waste chamber for receiving the solution from the second cartridge.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/833,702 (Attorney Docket No. 36312-708.201), filed Jul. 9, 2010,which claims the benefit of prior provisional application 61/270,571,filed on Jul. 9, 2009, the full disclosure of which is incorporatedherein by reference. The present application is also related to, butdoes not claim the benefit of, U.S. patent application Ser. No.12/406,670 (Attorney Docket No. 36312-705.201), filed on Mar. 18, 2009,now issued U.S. Pat. No. 8,162,917, the full disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to methods and apparatus forcombining parenteral solutions. More particularly, the present inventionrelates to methods for combining sodium bicarbonate and other bufferingsolutions with parenteral solutions stored in small cartridges.

Solutions containing bicarbonate ions are used in various medicalapplications such as antidotes, dialysates, artificial cerebrospinalfluid, intraocular irrigating solutions, cardiac perfusates,cardioplegic solutions, peritoneal irrigating solutions, and solutionsfor organ preservation, etc. Of particular interest to the presentapplication bicarbonate solutions are used to buffer the pH dentalanesthetic and other parenteral solutions. One of the most commonly usedmedical bicarbonate solutions consists of sodium bicarbonate (NaHCO₃)mixed with water (H₂O). In medical bicarbonate solutions, bicarbonateions are in equilibrium as represented by the following expression:

2HCO₃ ⁻

CO₂↑+CO₃ ²⁻+H₂O

If the reaction occurs in a closed system, equilibrium is between thepartial pressure of carbon dioxide in solution and the partial pressureof carbon dioxide in any space over the solution. In open systems atatmospheric pressure and room temperature, for instance where a beakerof sodium bicarbonate solution is left open in a lab environment, carbondioxide gas will continue to leave solution until the reaction hasproceeded almost completely to the right, or until almost all thebicarbonate (2HCO₃) has evolved into carbon dioxide gas (CO₂), carbonate(CO₃) and water (H₂O), and where all the CO₂ gas has left the openbeaker and entered the ambient air in the lab. Bicarbonate is more acidthan carbonate, meaning that the pH of the solution will haveprogressively moved toward the alkaline side of the pH scale. In fact,under these circumstances, the bicarbonate solution will achieve a pHover 9.5.

All commercially available medical sodium bicarbonate solutions aresupplied sterile in closed containers. All of them also have some amountof headspace into which, presumably, CO₂ could evolve out of solutionuntil an equilibrium between CO₂ evolving out of solution and going backin to solution, per the above equation, is reached. It could thereforebe hypothesized that the commercially available sodium bicarbonatesolutions have a pH that could exist in a fairly wide range. In fact thelabels on all commercially available medical bicarbonate solutionsstate, per the United States Pharmacopeia guidelines, that the pH can beanywhere from 7.0 to 8.5. An assay of a sample set of commerciallyavailable medical sodium bicarbonate solutions in a variety of volumesand containers may have pH range from 7.6 to 8.3 or more.

The pH of bicarbonate solutions is thus not a fixed figure, but rathercan exist at a range of levels dictated by the factors that tend to pushthe equilibrium equation, in a particular environment, either to theright or to the left, principally controlled by CO₂ leaving or enteringsolution.

Notably, in a closed container with no headspace, the pH of sodiumbicarbonate solution can be fixed by placing the solution having a knownstarting pH, in a sealed container under pressure that exceeds thepartial pressure of CO₂ in the solution, without a headspace. In thatenvironment, CO₂ will not evolve out of solution because pressure on thesolution is greater than the partial pressure of CO₂, and therefore thepH will not rise. Also in this environment where the pressure beingexerted on the solution is greater than the partial pressure of CO₂ insolution, because there is no headspace, and hence no available CO₂ gasthat can be driven into solution, the pH of the solution will notdecrease. In this model then, CO₂ does not leave or enter solution and,accordingly, the pH does not have the opportunity to either rise orfall. The pH of the solution in this system, is therefore, essentiallyfixed once the system is closed.

Even if the pH is known and fixed within a sealed container, asignificant pH change can be caused by the process of transferring thebicarbonate solution out of the container. Where the bicarbonatesolution is to be combined with another solution, as in anestheticbuffering, the process of mixing two solutions together can also includesteps that will create a greater or lesser pH change, which can affectthe predictability of the buffering process.

These considerations are important in buffering parenteral solutionsusing a syringe with a hypodermic needle to “draw up” bicarbonatesolution from a vial having a pierceable septum, and then mixing thebicarbonate with the target solution in order to alter the pH of thetarget solution. This vial and syringe system is typical and allows apractitioner to remove multiple doses of solution from a containerwithout opening the container or exposing it to the ambient air. Vialsthat are intended to be used in this manner necessarily include asignificant headspace, without which drawing up fluid in this mannercould not occur. When the vial contains a headspace, as the practitionerwithdraws the syringe's plunger, the headspace can expand to fill thespace vacated by the liquid that is leaving the vial, traveling throughthe hypodermic needle, and entering the barrel of the syringe. Ofcourse, as more and more solution is drawn up, for instance as multipledoses of the solution are used, the headspace expands more and more,continually lowering the gas pressure in that headspace.

Where a vial of this type contains bicarbonate that is removed in dosesusing a syringe, over time, because the partial pressure of the gas inthe headspace drops, the partial pressure of CO₂ in the headspace dropsas well, taking it out of equilibrium with the partial pressure of theCO₂ in solution. Per the equation set forth earlier, CO₂ gas will evolveout of solution to re-establish the equilibrium, which has the effect ofraising the pH of the bicarbonate solution each time a volume of thesolution is drawn up into a syringe. Whatever the starting pH of thevial's bicarbonate solution may have been, if it were known, the pH ofthe solution in the vial, after any amount of the solution has beenremoved in this manner, cannot be known. Therefore, if the pH of thesolution is an important element of its clinical utility, as when thebicarbonate is to be used for buffering the pH of a target solution suchas anesthetic, withdrawing bicarbonate from a vial using a syringe mayalter the pH to a degree that makes it difficult to predictably bufferany parenteral solution using this method.

Another concern when bicarbonate solution is drawn from a vial using asyringe is the effect of the vacuum created in the fluid path that leadsfrom the bicarbonate vial to the syringe. It has been observed that itis nearly impossible to draw up solution from a vial into a syringeusing a needle in the range typically employed for injections (25-30gauge) without creating gas in the syringe during the process. This isbecause the act of drawing the solution into the syringe creates avacuum on that solution that causes significant CO₂ to evolve out of thesolution that is being transferred. The resulting pH change, along withthe pH change that is occurring inside the vial with every withdrawal ofa dose of bicarbonate from the vial itself means that it is impossibleto know what the pH of the bicarbonate solution being used as a bufferis. With that lack of knowledge, the practitioner cannot control for thekey variable that would inform him or her as to how much bicarbonatesolution should be used in the buffering process. For this reason,buffering anesthetic using a vial of bicarbonate and a hypodermicsyringe is akin to a “home brew” where the results are not predictableand, in the case where the pH of the bicarbonate is too high, couldbuffer the anesthetic into a range where it can precipitate out ofsolution, making the buffered anesthetic dangerous.

Commonly-owned copending application US 2009/0292271 (application Ser.No. 12/406,670, previously incorporated herein by reference) describes a“dosing pen” device capable of combining buffers and anesthetics andovercoming many of the shortcomings of the prior art described above.The '271 application discloses a fluid transfer device which utilizes atransfer needle 36 and an exhaust needle 38 positioned in a knob 12which can removably receive an anesthetic cartridge 28 so that distalends of both the transfer needle and exhaust needle penetrate a septumon the anesthetic cartridge. A buffer cartridge 16 positioned within ahousing 14 is also attached to the knob 12 so that a proximal end 50 ofthe transfer needle 36 can penetrate a septum 15 of the buffer cartridgewhen the knob is fully advanced onto the housing. A pusher 20 isprovided to drive a plunger 58 on the buffer cartridge to transferbuffer through transfer needle 36 into the anesthetic cartridge 28 andto simultaneously exhaust anesthetic from the anesthetic cartridge backinto a reservoir 72 in the housing 14 through the exhaust needle 38.

While the dosing pen of the '271 application is advantageous in manyrespects, some improvements can be made such that a similar pen willprovide additional benefits. First, the dosing pen is designed to hold asingle buffer cartridge 16, and the design of the pen makes it difficultto replace the buffer cartridge. In particular, the pusher 20 isattached to the housing 14 to position an intermediate spring 18 againstthe plunger of the buffer cartridge, and a mechanism is provided whichdefines two advancement strokes to allow transfer of two pre-definedvolumes of buffer to one or two anesthetic cartridges. The pusherassembly is not easily disassembled, making replacement of the bufferdifficult. Thus, the entire pen must be disposed of after use.

Second, the pusher mechanism described above does not allow freeselection of a range of transfer volumes prior to use. The pushermechanism only allows two pre-defined volumes to be transferred by anyparticular pen construction. It would be desirable to allow a user toselect or “dial in” any volume in a given range without being limited tospecific preset values.

Third, the excess buffer, which is exhausted through exhaust needle 38,ends up in the housing 14. While it is theoretically possible to emptythe buffer and clean the housing (assuming the device could bedisassembled, which is difficult), it would be preferable if the excessbuffer were exhausted into another component of the system which couldeither be more easily cleaned or be disposed of while allowing othercomponents to be reused.

Fourth, removal of the first buffer cartridge from the dosing pen of the'271 application can be done without having removed the transfer needlefrom the buffer cartridge. Having a needle that can be left in aposition where it provides a fluid path open to the ambient air (that ispenetrating the septum of the buffer cartridge) could allow carbondioxide to evolve out of solution, thus potentially affecting the pH ofthe buffer.

For these reasons, it would be desirable to provide improved methods andapparatus for combining buffer solutions with anesthetics, particularlywhere the buffer solutions and/or anesthetics are held in conventionalglass cartridges with needle penetrable septums and dispensing plungers.It would be further desirable if such methods and apparatus could beused with other parenteral and medical solutions which are desired to becombined under carefully controlled conditions. The methods and deviceswould preferably allow for convenient buffering or dosing of multipleanesthetic or other cartridges from a single buffer or other medicalsolution cartridge. It would be still further desirable if the methodsand devices provided for a removal of a transfer needle from the bufferor other medical solution cartridge every time the anesthetic or otherrecipient cartridge was removed from the dosing apparatus. Stillfurther, it would be desirable if some components of the apparatus werereusable and the buffer cartridges replaceable. At least some of theseobjectives will be met by the inventions described hereinbelow.

2. Description of the Background Art

US2009/0292271 has been described above. Glass vials and cartridges forstoring medical solutions are described in U.S. Pat. Nos. 1,757,809;2,484,657; 4,259,956; 5,062,832; 5,137,528; 5,149,320; 5,226,901;5,330,426; and 6,022,337. Injection pens which employ drug cartridgesare described in U.S. Pat. No. 5,984,906. A particular disposable drugcartridge that can find use in the present invention is described inU.S. Pat. No. 5,603,695. A device for delivering a buffering agent intoan anesthetic cartridge using a transfer needle is described in U.S.Pat. No. 5,603,695. Devices for maintaining a dissolved gas in solutionin a pouch are described in U.S. Pat. Nos. 5,690,215; 5,610,170; and4,513,015, and U.S. Patent Publ. No. 2007/0265593. Other patents andapplications of interest include U.S. Pat. Nos. 2,604,095; 3,993,791;4,154,820; 4,630,727; 4,654,204; 4,756,838; 4,959,175; 5,296,242;5,383,324; 5,603,695; 5,609,838; 5,779,357; and U.S. Patent Publ. No.2004/0175437.

BRIEF SUMMARY OF THE INVENTION

The present invention provides methods and apparatus for combiningmedical or parenteral solutions, such as buffering anesthetics or othermedical or parenteral solutions held in a conventional cartridge,particularly those having a penetrable septum and a slidable plunger orplug, such as those generally described in US 2009/0292271, the fulldisclosure of which is incorporated herein by reference. Such cartridgesare commonly used in dental practice, particularly for deliveringanesthetics to a patient prior to a procedure. Such cartridges areconventionally loaded into a syringe or other delivery device, where thesyringe engages the plunger in the cartridge to dispense the anestheticthrough a needle which has penetrated the septum. To optimizeeffectiveness of the anesthetics and to reduce injection pain, it isdesirable to buffer conventional dental anesthetics, typicallylidocaine, articaine, prilocalne, or mepivacaine, shortly before use. Itis very important, however, that the buffering solutions themselves havepredictable, stable pHs and chemical compositions in order toaccurately, reliably, and safely buffer anesthetic to achieve a muchmore rapid onset, optimum effectiveness, and minimum injection pain.

Methods according to the present invention for buffering anestheticcartridges comprise providing a buffer cartridge having a septum and aplunger and providing an anesthetic cartridge having a septum and aplunger. The plunger end of the buffer cartridge is attached to one endof a cartridge connector so that a transfer needle which is part of thecartridge connector penetrates the septum of the buffer cartridge toestablish a flow path out of said cartridge. A septum end of theanesthetic cartridge is attached to the other end of the cartridgeconnector so that the transfer needle and an exhaust needle bothpenetrate the septum of the anesthetic. The transfer needle thusprovides a transfer flow path from the buffer cartridge to theanesthetic cartridge, while as described in more detail below, theexhaust needle provides a flowpath from the anesthetic cartridge to asealed interior waste chamber in the cartridge connector. By “sealedinterior waste chamber” it is meant that the waste chamber will receiveand hold excess volumes of the anesthetic which are displaced whenbuffer is transferred into the anesthetic cartridge. Usually, thechamber will have at least a small gas exhaust path to allow gas tobleed from the waste chamber as the liquid anesthetic enters thechamber.

In this way, when the user advances the buffer cartridge plunger totransfer a volume of buffer from the buffer cartridge into theanesthetic cartridge, a like volume of anesthetic will be displaced fromthe anesthetic cartridge into the waste chamber in the cartridgeconnector where it will be sequestered until the cartridge connector isemptied or disposed of.

It is a particular advantage of the present invention that theanesthetic cartridge may be removed from the cartridge connector after adesired volume of buffer has been transferred from the buffer cartridgeto the anesthetic cartridge. In particular, the cartridge connector canbe configured so that the transfer needle must be removed from thebuffer cartridge before the anesthetic cartridge can be removed from thecartridge connector. In this way, the buffer remains sealed (the septumseals after the transfer needle is removed) within the buffer cartridgeand is not exposed to the ambient or atmosphere through the transferneedle when the anesthetic cartridge has been removed and the remote endof the transfer needle is open to the atmosphere. Once the anestheticcartridge has been removed, the cartridge connector and other apparatusremain available for attachment to a second anesthetic cartridge for anextended period of time, since the buffer remains sealed within thebuffer cartridge. After a second anesthetic cartridge is attached againto the cartridge connector, the plunger on the upper cartridge may befurther advanced to transfer an additional volume of buffer to thesecond anesthetic cartridge. The second anesthetic cartridge can then beremoved from the cartridge connector with the transfer needle againbeing withdrawn from the septum of the buffer cartridge to preserve thepH of the buffer and additional anesthetic cartridges inserted until thebuffer is used up.

The methods of the present invention further allow for different volumesof buffer to be delivered to the different anesthetic cartridges whichare sequentially replaced and attached to the cartridge connector. Forexample but not by way of limitation, volumes in 0.01 increments in therange from 0.01 ml to 0.60 could be selected and “dialed in” to a devicewhich advances the buffer cartridge plunger to deliver any volumeincrement in that range, in contrast to the limited number ofpre-selected volumes deliverable by the devices of the '271 applicationdiscussed above.

In a still further aspect of the present invention, the amount of bufferremaining in the buffer cartridge will be visible to the user so thatthe same buffer cartridge can be used multiple times until the buffercartridge is empty, or until so small a volume remains that it is nolonger usable. In such cases, the cartridge connector will havecollected a significant volume of anesthetic of other parenteralsolution being buffered. It will usually be desirable to dispose of thecartridge connector and to later employ a new, sterile cartridgeconnector with other components of the system (as described below).

In particular aspects of the methods of the present invention, thecartridge connector is manipulated by removably attaching the connectorto a cartridge holder which holds the buffer cartridge. The cartridgeconnector is thus attached at one end to the cartridge holder andincludes a sleeve or receptacle at the other end for removably receivingthe anesthetic cartridge. Usually, the cartridge holder will have awindow which allows visual observation of the contents of the buffercartridge during use. A separate plunger driver may be attached to anopposite end of the cartridge holder for engaging a plunger on thebuffer cartridge to controllably dispense and transfer preselectedvolumes of the buffer to the anesthetic cartridge.

The present invention further provides devices for transferring a volumeof solution from a first cartridge having a septum to another solutionin a second cartridge having a septum. The device comprises a cartridgeholder, a plunger driver, and a cartridge connector. The cartridgeholder has a proximal end, a distal end, and a chamber for removablyreceiving the first cartridge, which is typically a buffer, such as asodium bicarbonate buffer as described in more detail above. The plungerdriver is attachable to the proximal end of the cartridge holder and hasa piston rod which engages a plunger on the first cartridge, where thepiston rod is controllable to axially advance the plunger to deliverpre-selected “dialed-in” volumes of the content of the first cartridge.Such plunger drivers are commercially available from suppliers such asHaselmeier GmbH, St. Gallen, Switzerland. As used in the presentinvention, such plunger drivers will have a mechanism which allows avariable volume to be selected and delivered, typically by rotating aknob which displays the volume in a window, and further includes abutton which may be depressed for advancing the piston rod to cause thepiston rod to travel a distance which will dispense the desired volumeof liquid from the first cartridge.

The cartridge connector of the present invention has a proximal endwhich is attachable to the distal end of the cartridge holder and adistal end which is adapted to engage a septum end of the secondcartridge. The cartridge connector will further have a sealed interiorwaste chamber and includes a transfer needle and an exhaust needle. Thetransfer needle extends from one end of the cartridge connector to theother so that it will penetrate through a septum of the first (e.g.buffer) cartridge at one end and through a septum of the second (e.g.anesthetic) cartridge at the other end. The exhaust needle extends fromthe second cartridge and terminates within the interior waste chamber.In this way, as described in connection with the method of the presentinvention, advancement of the plunger in the first cartridge transferssolution into the second cartridge and further causes the solution inthe second cartridge to be exhausted through the exhaust needle into theinterior waste chamber.

The cartridge holder has a body, typically cylindrical, with a window toallow visual observation of the contents of the cartridge in thecartridge holder. In this way, the user can see when the first cartridgeis running low and needs to be replaced. A distal region of thecylindrical body is typically enlarged to removably receive thecartridge connector, and the cartridge connector will typically beinterlocked so that the transfer needle can penetrate the firstcartridge (held within the cartridge holder) only when the secondcartridge is placed over the other end of the transfer needle.

The cartridge connector will usually also comprise a cylindrical body,and the cylindrical body will typically be removably received within theenlarged end of the distal region of the cartridge holder. The sealedinterior waste chamber of the cartridge connector is defined betweenspaced-apart walls in the cylindrical body of the cartridge connector,and usually a first end of the cylindrical body will form a cylindricalsleeve which surrounds the exposed ends of the exhaust needle and thetransfer needle, where the sleeve is adapted to removably receive theseptum end of the second cartridge.

The present invention still further provides a cartridge connector forproviding or establishing fluid transfer paths between a first cartridgehaving a septum and a second cartridge having a septum. The cartridgeconnector comprises a body having a first end, a second end, and asealed interior waste chamber. A transfer needle has a first end exposedat a first end of the body and a second end exposed at a second end ofthe body. Both the first and second ends of the transfer needle arecapable of penetrating a cartridge septum. An exhaust needle is providedon the body and has a first end exposed at the first end of the body anda second end terminating in the sealed interior waste chamber. At leastthe first end of the exhaust needle is capable of penetrating acartridge septum.

The first end of the cartridge connector will typically include acylindrical sleeve or similar structure surrounding the exposed ends ofthe transfer needle and the exhaust needle. The cylindrical sleeve willbe adapted to removably receive the septum of a cartridge, typically ananesthetic cartridge. Usually, the first end of the transfer needle isaxially spaced-apart from the first end of the exhaust needle so thatthe material being exhausted will be segregated from the material beingtransferred in through the transfer needle. Usually, the transfer needlewill be axially or otherwise disposed through the sealed interior wastechamber, and the second end of the transfer needle will be free fromsurrounding structure. Usually, the cartridge connector will be providedas a separate sterile component of the devices and systems describedherein and will be provided with a separate removable cap for placingover the exposed second end of the transfer needle for safety.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a dosing pen system constructed in accordancewith the principles of the present invention and having a buffercartridge and an anesthetic cartridge attached.

FIG. 2 is a perspective view of the dosing pen system of FIG. 1.

FIG. 3 is an exploded view of the dosing pen system of FIGS. 1 and 2illustrating each of the components separately.

FIG. 4 illustrates the cartridge connector of the dosing pen system ofFIGS. 1-3, including a safety cap for protecting an exposed end of atransfer needle.

FIG. 5 is an axial cross-sectional view of the cartridge connector ofthe dosing pen of the present invention illustrating the relativepositions of the transfer needle, the exhaust needle, and a sealedinterior waste chamber thereof.

FIGS. 6 and 7 illustrate the attachment of a first (buffer) cartridgeand a second (anesthetic) cartridge to the cartridge connector of FIG.5.

FIG. 8 illustrates the manual actuation of the dosing pen system of thepresent invention.

FIG. 9 illustrates the fluid transfer flow between a first (buffer)cartridge, second (anesthetic) cartridge, and sealed interior wastechamber caused by the manual actuation of the dosing pen system.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIGS. 1 and 2, a dosing pen system 10 includes a cartridgeholder 12, a plunger driver 14, and a cartridge connector 16. Thecartridge connector 16 is removably received in an enlarged distal end18 of the cartridge holder 12, and the plunger driver 14 includes apiston rod 20 which drives a plunger 22 on a first (buffer) cartridge 24(best seen in FIG. 3) which is observable through a window 26 through awall of the cartridge holder 12.

The plunger driver 14 may be obtained as a pre-assembled unit fromcommercial vendors. In particular, Haselmeier GmbH, article number435300, is suitable for use in the present invention.

Referring now to FIG. 3, an anesthetic cartridge 30 is inserted througha distal end 32 of the cartridge connector 16, as will be described ingreater detail below with respect to FIGS. 5-7. The cartridge connector16, in turn, is inserted in through distal end 34 of the cartridgeholder 12 so that it is received in the enlarged distal end 18. Thebuffer cartridge 24 is inserted in through a proximal end 36 of thecartridge holder 12 so that it is visible through the window 26 and aseptum end penetrates needles of the cartridge connector 16, asdescribed in more detail with respect to FIGS. 6 and 7 below. Finally,the plunger driver 14 is attached to the proximal end 36 of thecartridge holder 12, typically using a threaded or similar connector 38at a distal end of the plunger driver. With all the connections justdescribed, the dosing pen 10 is in the configuration illustrated inFIGS. 1 and 2.

Referring now to FIG. 4, the cartridge connector 16 will typically beprovided with a removable cover or cap 40 which protects an exposed end42 of transfer needle 44, as seen in FIGS. 5-7. The cap 40 is providedto protect personnel handling the connector. Typically, the cartridgeconnector 16 will be provided as a sterile component with the cap 40attached over the exposed end 42 of needle 44, usually in a sterilepack, such as a pouch. The remaining components of the dosing pen, andin particular the cartridge holder 12 and the plunger driver 14 willtypically be reusable and will not need to be maintained in or returnedto a sterile condition. Typically, cleaning with conventional cleaningagents is sufficient between successive uses. As the cartridge connector16 is the only system component which directly contacts the buffer,anesthetic, or other parenteral solutions, the sterility of thesesolutions can be maintained so long as the sterility of the cartridgeconnector is maintained.

Referring now to FIG. 5, the cartridge connector 16 comprises acylindrical body 50, typically formed from a molded plastic such as ABS,and includes at least one interior chamber 52 (which may be divided intomore chambers and/or may include vents, membranes, absorptive materialsor other features). The cylindrical body 50 will also usually include anopen region or sleeve segment 54 which is adapted to receive the septumend of the anesthetic cartridge 30. The transfer needle 44 extends fromproximal end 56 of the cylindrical body 50 to a position within theinterior of the open region 54. An exhaust needle 60 has one end withinthe open region 54 and another end terminating within the sealed chamber52. Sealed chamber 52 will receive anesthetic or other solution which isbeing exhausted from the first cartridge 30 as buffer or other solutionsare transferred into the first cartridge. The sealed chamber 52 willtypically be liquid tight but may have gaseous exhaust paths so that theliquid may fill the chamber while exhausting air or other gasesinitially present within the chamber. Such exhaust paths can be providedby having capillary exhaust paths formed in the chamber which allow gasto vent while preventing liquid passage.

As shown in FIGS. 6 and 7, the buffer cartridge 24 is attached to theexposed end 42 of transfer needle 44 by advancing the sharpened end ofthe needle through the septum end 64 of the first cartridge, as shown inFIG. 7. Similarly, the septum end 66 of the second cartridge 30 isadvanced over the ends of the transfer needle 44 and exhaust needle 60,as shown in FIG. 7.

In a specific aspect of the present invention, attachment of the second(anesthetic) cartridge 30 to the transfer needle 44 and exhaust needle60 can be interlocked with the presence of the exposed end 42 of thetransfer needle in the first (buffer) cartridge 44. In particular, it isdesirable that the transfer needle 44 be removed from the firstcartridge if and when the second cartridge is removed from the cartridgeconnector. This can be achieved, for example, by providing a series offorce fit connections of declining relative strength between the secondcartridge and the cartridge connector 16. Thus, when the practitionerpulls the second cartridge distally away from the cartridge connector 16and first cartridge 24, the force fit between the cartridge connectorhousing and the first cartridge 24 is first to release because it is theweakest force fit. This allows the transfer needle to move away from thefirst cartridge and disconnect from the first cartridge after a dosingevent. The transfer needle may travel until it hits a distal stop. Whenthe transfer needle can no longer move distally, the second cartridgewill disconnect from the cartridge connector. When another second(anesthetic) cartridge is connected to the cartridge connector 16, theprocess of inserting the transfer needle back into the buffer cartridgecan be reversed. In this way, when no second (anesthetic) cartridge ispresent when the transfer needle is open to the atmosphere, the transferneedle will necessarily have been removed from the first (buffer)cartridge so that the pH cannot be disturbed.

Referring to FIG. 8, a user can transfer buffer or other parenteralsolution to an anesthetic or other parenteral solution by connecting thecartridges 24 and 30 to the cartridge connector 16 as generally shown inFIGS. 1-3, 6, and 7. The user then turns knob 70 on the plunger driver14 to choose the desired transfer volume, as shown in window 72. Oncethe volume is “dialed in”, the user can press the knob 40 using thumb Tin order to advance the piston rod 20 a distance determined by the knobrotation which corresponds to the desired volume. After transferring adesired target volume of buffer or other solution into cartridge 30, thecartridge 30 may be removed and replaced with another cartridge to whichthe buffer or other solution is to be transferred. The desired transfervolume can then be dialed in and the knob depressed to transfer thebuffer to the second cartridge. This process can be continued withfurther cartridges until the volume of buffer or other solution incartridge 24 is depleted, as can be seen through window 24 when plunger22 reaches the far left of the window 26, as shown in FIG. 1.

As shown in FIG. 9, depressing the plunger causes buffer or othersolution from cartridge 24 to flow through transfer needle 44 and intocartridge 30, as indicated by arrow 74. As the cartridge 30 has a fixedvolume and is usually full of fluid, the entry of buffer or other fluidwill cause an excess volume which is exhausted through exhaust needle60, in the direction of arrow 76. The ends of transfer needle 44 andexhaust needle 60 may be offset from each other, to the degree shown orto a greater or lesser degree, so that solution that is delivered bytransfer needle 44 is limited in its tendency to be captured andexpelled through exhaust needle 60. Exhaust chamber 52 can receive asignificant volume of the exhausted anesthetic or other solution beforeit is full. After it is full, it either needs to be disposed of oremptied.

While the above is a complete description of the preferred embodimentsof the invention, various alternatives, modifications, and equivalentsmay be used. Therefore, the above description should not be taken aslimiting the scope of the invention which is defined by the appendedclaims.

What is claimed is:
 1. A device for transferring a volume of a solutionfrom a first cartridge having a septum to another solution in a secondcartridge having a septum, said device comprising: a cartridge holderhaving a proximal end, a distal end, and a chamber for removably holdingthe first cartridge; a plunger driver removably attachable to theproximal end of the cartridge holder and having a piston rod whichengages a plunger on the first cartridge; and a cartridge connectorhaving a proximal end attachable to the distal end of the cartridgeholder, a distal end adapted to engage a septum end of the secondcartridge, said cartridge connector including a transfer needle and anexhaust needle which extend distally to penetrate the septum end of thesecond cartridge, wherein the transfer needle extends proximally topenetrate the septum of the first cartridge and the exhaust needleterminates in the sealed interior waste chamber; wherein after use, theplunger driver may be removed from the cartridge holder, the firstcartridge removed, and the cartridge holder and plunger cleaned forre-use.
 2. A device as in claim 1, wherein the cartridge connector hasan interior waste chamber which is configured to receive waste solutionfrom the second cartridge which is displaced from the second cartridgeas fluid from the first cartridge is transferred.
 3. A device as inclaim 1, wherein the cartridge holder has a cylindrical body with awindow to allow visual observation of the contents of the firstcartridge in the cartridge holder.
 4. A device as in claim 3, wherein adistal region of the cylindrical body is enlarged to removably receivethe cartridge connector.
 5. A device as in claim 1, wherein the plungerdriver is adjustable so that the length of travel of the piston rod canbe selected prior to advancement of said piston rod.
 5. A device as inclaim 4, wherein the cartridge connector comprises a cylindrical bodythat is removably received within the enlarged distal region of thecartridge holder.
 6. A device as in claim 2, wherein the sealed interiorwaste chamber is defined between spaced-apart wells in the cylindricalbody of the cartridge connector.
 7. A device as in claim 3, wherein thefirst end of the cylindrical body forms a cylindrical sleeve whichsurrounds the exposed ends of the exhaust needle and the transferneedle, wherein said sleeve is adapted to receive the septum end of acartridge.
 8. A device as in claim 7, wherein the first end of thetransfer needle is axially spaced-apart from the first end of theexhaust needle.
 9. A device as in claim 16, wherein the transfer needlepasses axially through the sealed interior waste chamber.
 10. A deviceas in claim 9, wherein the second end of the transfer needle is free ofsurrounding structure, said connector further including a removable capfor placing over the exposed second end of the transfer needle.
 11. Amethod for buffering an anesthetic cartridge, said method comprising:(a) removably inserting a first buffer cartridge having a septum and aplunger into a chamber of a cartridge holder; (b) attaching a plungerdriver to a proximal end of the cartridge holder; (c) attaching a oneend of a cartridge connector to a distal end of the cartridge holder sothat a transfer needle penetrates the septum of the buffer cartridge;(d) attaching a first anesthetic cartridge to another end of thecartridge connector so that the transfer needle and an exhaust needlepenetrate the septum of the first anesthetic cartridge; (e) advancing aplunger on the plunger driver to engage the plunger on the buffercartridge to transfer a volume of buffer from the first buffer cartridgeinto the first anesthetic cartridge and exhaust a volume of anestheticfrom the first anesthetic cartridge; (f) removing the first anestheticcartridge from the cartridge connector for use; (g) optionallyconnecting another anesthetic cartridge to the cartridge connector andrepeating step (e) one or more times; and (h) when done with the firstbuffer cartridge, removing the plunger driver and the first buffercartridge and cleaning the cartridge holder and plunger driver forre-use.
 12. A method as in claim 1, further comprising disposing of thecartridge connector.
 13. A method as in claim 12, wherein the cartridgeconnector contains the exhausted anesthetic.
 14. A method as in claim11, wherein additional anesthetic cartridges are sequentially replacedon the cartridge connector and volumes of buffer transferred to saidadditional anesthetic cartridges until the buffer cartridge is empty.15. A method as in claim 14, further comprising visually observing thebuffer cartridge to determine when said buffer cartridge is empty.
 16. Amethod as in claim 15, wherein the cartridge holder has a window thatallows visual observation of the contents of the buffer cartridge.